Friction welding apparatus

ABSTRACT

Method and apparatus for friction welding two rotating end workpieces to a non-rotatable central workpiece wherein one end workpiece is held axially stationary while the other end workpiece is moved axially into engagement with the central workpiece and then axially displaces the central workpiece into engagement with the one end workpiece. The central workpiece is mounted on a floating table which is axially displaceable to accomplish the described welding cycle.

O Umted States Patent [191 [111 3,776,446

Gage et al. Dec. 4, 1973 [54] FRICTION WELDING APPARATUS 3,238,6123/1966 Herman 228/2 1 Arthur n Warren; Alex 31333132 13/1323 313$ Z2 21113............3311135333? Stamm, Rochester, both of Mich.

[ 1 Assignoo: Rockwell International Corporation, PrimaryExaminer-Robert D. Baldwin Pitts u gh, Pa- Assistant Examiner-Robert JCraig [22] Filed: Jam 5, 1973 Attorney-John R. Bronaugh et al.

App]. No.: 321,489

Related US. Application Data Division of Ser. No. 151,767, June 10,1971, Pat. No. 3,727,298.

US. Cl 228/2, 29/4703, 156/73 Int. Cl B23k 27/00 Field of Search 228/2;29/4703;

References Cited UNITED STATES PATENTS 2/1966 Hollander 228/2 X [57]ABSTRACT Method and apparatus for friction welding two rotating endworkpieces to a non-rotatable central workpiece wherein one endworkpiece is held axially stationary while the other end workpiece ismoved axially into engagement with the central workpiece and thenaxially displaces the central workpiece into engatement with the one endworkpiece. The central workpiece is mounted on a floating table which isaxially displaceable to accomplish the described welding cycle.

6 Claims, 2 Drawing Figures PATENIED 75 SHEET 2 OF 2 Em 32 f in lavaN653:

wv 3v 3 Q 8 @5755 D m w? Sm $2 mmw x I T om V wm im SN D ES FRICTIONWELDING APPARATUS This is a division, of US. Pat. application Ser. No.151,767, filed June 10, 1971 now US. Pat. NO. 3,727,298.

FIELD OF INVENTION This invention relates generally to apparatus forfriction welding workpieces together, and more particularly, toapparatus for friction welding the parts of an axle drive housingtogether, that is, friction welding a pair of end spindles onto a centeraxle housing section.

SUMMARY OF THE INVENTION The primary object of this invention resides inthe provision of a novel apparatus for friction welding workpiecestogether.

Another object of the invention resides in the provision of a novelapparatus for friction welding a pair of end workpieces to a centerworkpiece by axially engaging and forcing the workpieces together.

Still another object of the invention resides in the provision of anovel method for friction welding the parts of an axle drive housingtogether, wherein the end spindles are rotated relative to the centerhousing section and, during the weld cycle, one of the end spindles ismaintained axially stationary while the other end spindle and centerhousing section are axially displaced to effect engagement between thethree workpieces under a high axial thrust to friction weld the threepieces together.

A further object of the invention resides in the provision of a novelapparatus for friction welding the parts of an axle drive housingtogether by mounting the center axle housing section on a floatingslidable table, and during the weld cycle, maintaining one ofthe endspindles axially stationary while the other end spindle and centersection are displaced axially to effect engagement between each of theend spindles and center section and thereby frictionally weld the threeworkpieces together.

Still other objects and advantages of the invention will become apparentfrom reading the following detailed description of the invention withreference to the accompanying drawings, with the scope of the invention,however, being limited only by the appended claims.

. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of afriction welding apparatus that may be used to accomplish the method ofthis invention; and

FIG. 2 is a schematic illustration of a hydraulic control circuit forcontrolling the axial displacement of the end workpieces and centralworkpiece during a welding operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT ary while workpiece 13 is movedaxially to the left into engagement with arm 12b of center section 12,whereupon center section 12 is then also moved to the left until itsother arm 12a engages workpiece 11, thereby friction welding the threeworkpieces together.

Center section 12 is mounted on a cradeling table structure 14 whereonopposite sides of the workpiece are engaged and held suitable byadjustable jaws l5 and 16. The opposite extending arms 12a and 12b ofworkpiece 12 are clamped tightly in similar fixtures 17, which grip andfix the arms against rotation and axial movement on table 14. The table14 is axially slidably mounted on guide rails 18 and 19 which extendsubstantially throughout the length of the friction welding apparatus.

Workpiece 11 is mounted within a hydrostatic bearing unit carrier 22,which has a frame 24 slidably mounted on rails 18 and 19. Similarlyworkpiece 13 is mounted in a hydrostatic bearing unit carrier 23, havinga frame 25 which is also slidable along the guide rails 18 and 19.

Carrier frame 24 is axially displaceable along guide rails 18 and 19 byway of a pair of hydraulic cylinders 26 and 28, the piston rods 30 and32 of which arre connected to the frame 24 for axially displacing theworkpiece 11 on rails 18 and 19 toward center section 12. Within carrierunti 22, workpiece l 1 is drive connected to a rotatable shaft 34axially slidable within drive pulley 36 via a spline connection, withthe pulley 36 being driven from a drive assembly 38 via belt 40 torotate the workpiece 11 during the weld cycle.

Similarly, the carrier unit 23 is axially displaceable by way of a pairof hydraulic piston cylinders 42 and 44, the piston rods 46'and 48 ofwhich are connected to the carrier support 25 for moving the supportaxially along guide rails 18 and 19. Within carrier unit 23, workpiece13 is drive connected to a rotatable shaft 50 which is slidable within apulley 52 via a spline connection, with the pulley 52 being rotated froma drive system 54 via belt connection 56.

It should be noted that cylinders 26 and 28 are larger in diameter thancylinders 42 and 44, and the purpose for this difference will becomeapparent hereinbelow.

For a more detailed description of the carrier units 22 and 23 and theirrespective drive systems, reference may be had to US. Pat. applicationSer. No. 753,214, filed on Aug. 16, 1968, which application is assignedto the assignee ofthis invention.

Briefly, initially the carriers 22 and 23 will be positioned in theirextreme retracted end positions to permit loading of the workpieces 11and 13 therein and to permit placement of the center section 12 on thetable 14. When the loading is completed, workpieces l1 and 13 will berotated from the drive systems 38 and 54 and the hydraulic controlcircuit illustrated in FIG. 2 will be motivated to move the carrier unit22 and workpiece 11 to the right until the pistons within hydrauliccylinders 26 and 28 bottom out, i.e., engage against the inboard ends-ofcylinders 26 and 28, to position the end of workpiece 11 at apredetermined start position A. Table 14 and the center housing section12 mounted thereon will also be moved to the right to a predeterminedstart position shown in FIG. 1, established by the adjustable stopmembers 60 and 62 which are fixed adjacent the guide rails 18 and 19 toabut the table 14. When workpieces 11 and 12 are so located in theirstart" positions, the opposing ends of workpiece ll and arm 120 will belocated respectively at positions A & B and separated a distance C.Carrier unit 23 and workpiece 13 will also be moved to the left towardthe arm 12b of center section 12.

The stop members 60 and 62 which establish the initial start position oftable 14 are adjusted so that when the pistons in cylinders 26 and 28reach their forward end positions and bottom out, the end of workpiece11 is spaced a predetermined distance C, for example, A A inches fromthe opposing end face of arm 12a, so that initially there is no contactbetween workpiece 11 and arm 12a. Also, the travel speed of unit carrier23 and workpiece 13 is adjusted by the cylinders 42 and 44 so that table14 will engage stops 60 and 62 and cylinders 26 and 28 will bottom out,thereby fixing the start positions of table 14 and workpiece 11, beforethe workpiece 13 contacts the opposing face of arm 12b. Thereafter, therotating workpiece 13 continues to be moved axially by cylinders 42 and44 into engagement with arm 12b and then causes axial displacement oftable 14 to the left on rails 18 and 19 so that the arm 12a will bemoved into engagement with the rotating workpiece 1 1, which is held ina fixed axial position by the hydraulic pressure within cylinders 26 and28.

The high speed of rotation of workpieces 11 and 13 against thenon-rotatable fixed arms 12a and 12b, and the axial thrust with whichthe three workpieces are forced together causes the metal of theengaging faces of the workpiece to become plastic. Subsequently,rotation of the workpieces is stopped and the plasticized metal allowedto cool to form the weld sections between the workpieces 11, 12 and 13.When the weld sections have cooled, the workpieces l l and 13 arereleased from carrier units 22 and 23, which are then retracted to theirload positions in readiness for the next welding cycle.

Referring now to FIG. 2, a typical hydraulic control circuit will bedescribed for operating the welding apparatus of FIG. 1 andaccomplishing the method of operation briefly set forth above.

Assume carrier units 22 and 23 are retracted to their load positions inwhich suitable workpieces 11 and 13 are mounted in the units and acenter workpiece 12 is clamped on table 14. In this position, pistons26a and 28a will be bottomed against the outboard ends (left ends) ofcylinders 26 and 28 and pistons 42a and 44a will be positioned adjacentthe outboard ends (right ends) of cylinders 42 and 44. When loadedworkpieces 11 and 13 will be rotated by energization of drive assemblies38 and 54.

With solenoids S1A, SIB initially de-energized and solenoids S2A, 82Band S38 energized, the valves controlled thereby will be positioned asshown in FIG. 2. Valve 104 is shown when solenoid S4A is de-energized.However, initially solenoid S4A will be energized and valve 104 will bein its other flow blocking position.

The welding cycle will proceed as follows, with movement of carrier 22being described first. Pump 70 will drive fluid oil from a reservoirsump 72 and pass it via conduit 74, a spring-biased, solenoid operatedfour way valve 76 operated by solenoid S2A, conduit 78, one outlet portof a spring biased, solenoid operated valve 80 operated by solenoid S1A,and conduit 82 to the outboard end of cylinder 28 which isinterconnected with the outboard end of cylinder 26 via conduit 84. Theinboard ends of cylinders 26 and 28 are interconnected by conduit 86.

Another outlet port from valve is also connected via conduit 95, and inthe illustrated position of valve 80 serves to connect a conduit 134 tosump 72. In the other position of valve 80, conduit 87 will connectconduit 78 to sump 72.

The fluid provided at the outboard ends of cylinders 26 and 28 willcause pistons 26a and 28a to be displaced to the right, thereby slidingcarrier 22 along guides 18 and 19 to the right. The fluid ahead of thepistons will drain through a conduit 88, the outlet port of valve 76,conduit 90, and a solenoid operated valve 92 operated by solenoid S3A,with valve 92 in its illustrated position being connected to the sump 72via conduits'94 and 95, check valve 96, and heat exchanger 98. Checkvalve 96 serves to maintain a low pressure of about 50-75 psig in theoil return conduit as a pilot source for the various solenoid operatedvalves.

Carrier 22 will thus proceed to the right at a rapid travel rateestablished by the rate of oil flow to the outboard ends of cylinders 26and 28. This rate of oil flow is determined by the oil displacement ofpump 70 and the setting of a flow relief valve 100. Valve 100 ispositioned with its inlet port connected by a conduit 108 to conduit 74between valve 76 and pump 70. One of the outlet ports of valve 100 isconnected by a conduit 108 to conduit 74 between valve 76 and pump 70.One of the outlet ports of valve 100 is connected by a conduit 110 toconduit 87. The setting of relief valve 100 is sufficiently high that nofluid flow will occur therethrough as long as pistons 26a and 280 havenot bottomed out and carrier 22 is moving towards the right. Rapidtravel of carrier 22 thus is achieved because the full displacement ofpump 70 is directed to the outboard ends of cylinders 26 and 28 andfluid flow from the inboard ends of this cylinder is unrestrictedbecause valve 92 is open.

The rapid travel rate of carrier 22 will continue until limit switchLS2A is activated by frame 24 and the rate of flow of oil to cylinders26 and 28 to reduced to effect the slower, creep rate of travel ofcarrier 22 until pistons 26a and 28a bottom out or engage against theinborad ends of cylinders 26 and 28 and the end of workpiece 11 islocated at its predetermined weld position indicated by the referenceline A in FIG. 1. To control the rate of oil flow rate into cylinders 26and 28 for slowing the travel of carrier 22 to the creep rate, a reliefvalve 102, a solenoid-operated valve 104 and a variable pressuretemperature compensated restrictor 106 are provided.

A vent control passage 112 operatively associated with valves 100 and104 is connected between a pilot valve (not shown) in valve 100 andvalve 104. Valve 104 has two outlet ports, one of which is blocked as at114 and the other of which is connected by a conduit 116 to the inletport of relief valve 102. The outlet port of valve 102 is connected by aconduit 118 to conduit 87.

Restrictor 106 is disposed in a bypass conduit 120 which is connectedbetween conduits 90 and 94. When valve 92 is shifted to itsflow-blocking position established by blocking element 93, circulationof return oil is from conduit 90 through restrictor 106 to conduit 94.

Valve 104 that is in a flow blocking position during rapid travel ofcarrier 22 is operated by solenoid S4A which, when de-energized uponactivation of limit switch LSZA, allows valve 104 to be spring biased toits illustrated position where it connects passage 112 to conduit 116.Under this condition, relief valve 102 operatively is connected to oilinput conduit 74. The setting of valve 102 is such that a greater volumeof oil is bled off when valve 104 is open than when only relief valve100 is connected to conduit 74. Thus the volume of oil flowing tocylinders 26 and 28 markedly is lessened when valve 104 is open.

Further, upon the activation of limit switch LS2A, solenoid S3A isde-energized, and flow through valve 92 is blocked. Flow controlrestrictor 106 thus is placed in the exhaust circuit from the inboardends of cylinders 26 and 28 and functions to retard the flow rate of oilfrom these cylinders until the pistons 26a and 28a have bottomed out atthe right extremes of their cylinders.

From the foregoing it is clear that when initially solenoids S4A and S2Aare energized and when solenoid SlA is de-energized, oil will besupplied to the outboard ends of cylinders 26 and 28 at a relativelyhigh rate of flow. At this stage, solenoid S3A will also be energized toprovide a relatively unrestricted discharge path for quickly exhaustingthe oil at the inboard sides of pistons 26a and 28a. As a result,carrier 22 is advanced forwardly quite rapidly from its retractedloading position.

As carrier 22 approaches the position where pistons 26a and 28a areabout to engage the inboard end of cylinders 26 and 28 and end spindle11 is about to reach the predetermined start position A., the limitswitch LS2A is activated and solenoids 54A and S3A are deenergized. Asdescribed above, the pressure relief valves then function to limit theflow of oil to the outboard sides of pistons 26a and 28a whilesimultaneously de-energization of solenoid S3A allows valve 92 to bespring biased to its position where it blocks oil flow from conduit 90to conduit 94. The oil being exhausted from the inboard ends ofcylinders 26 and 28 consequently must flow through restrictor 106. Thisretards the rate of oil discharge from the inboard ends of cylinders 26and 28 to thereby increase the back pres sure acting on the inboardsides of pistons 26a and 28a. This rapidly decelerates the forwardadvancement of carrier 22 to slow it down in a relatively short distanceand thus allow pistons 26a and 28a to gently contact the inboard ends ofcylinders 26 and 28 and stop sliding movement of carrier 22. The end ofspindle 11 is then located at position A.

As described previously, the slidable table 14, is initially movedtoward the right to a predetermined position on guides 18 and 19 inengagement with stops 60 and 62 so that the end of arm 12a will belocated at a position B and spaced a predetermined distance C from theend of spindle 11 located at position A when pistons 26a and 28a arebottomed. The distance C is preferably about to A inches.

An actuating cylinder 120 has a piston 122 whose rod is connected totable 14. One end of cylinder 120 is connected via conduit 124 tocylinder 74 between pump 70 and valve 76, and the other end of cylinder120 is connected to drain conduit 87 via conduit 126. Thus, when pump 70is initially energized, oil will flow through conduit 124 to displacepiston 122 and table 14 to the right until the table engages the stops60 and 62. The table is then held in this position by cylinder 120 aslong as pump and conduit 74 remain connected to cylinders 26 and 28.

The hydraulic control system for controlling the movement of pistons 42aand 44a, and likewise the sliding movement of carrier 23 and spindle 13,is essentially a duplicate of that described for pistons 26a and 28a andlike elements are indicated by like numerals followed by the letter a.

Thus, initially oil from an adjustable variable displacement pump 130passes through a conduit 74a and valves 76a and 80a to the outboard endsof cylinders 42 and 44, thereby causing pistons 42a and 44a to move tothe left at a rapid travel rate. When limit switch LS2B is activated bycarrier frame 25, solenoids S38 and 84B will be de-energized and valves92a and 104a positioned to decrease the rate of oil flow in conduit 74aand place flow restrictor 106a into the cylinder exhaust circuit tothereby cause pistons 42a and 44a and carrier 23 to move at a slowercreep rate. In this way, the end of rotating spindle 13 will gentlyengage the end of arm 12b. After engagement of the opposing ends ofspindle 13 and arm 1212, a timer (not shown) energiz/es solenoids SlAand SIB a fixed increment of time, such as one second, after theactuation of limit switches LS2A and LSZB to move valves 80 and 80a totheir other operating positions in which conduit 78 and 78a areconnected to the drain conduits 87 and 87a and the oil from pumps 70 andis merely circulated back to sump 72.

Up to this time, oil from a high pressure weld pump 132 will have passedthrough conduit 134 through the de-energized valves 80 and 80a toconduits 87 and 87a back to sump 72. It is desirable that oil from pump132 pass through a modulator unit 136 positioned in conduit 134 prior toarriving at valves 80 and 80a. Modulator 136 comprises no part of thepresent invention and reference hereby is made to said US. Pat.application No. 753,214 for details of the construction and function ofthis modulator.

However, when solenoids 81A and SIB are energized and valves 80 and 80aare moved to their operating positions, the higher pressure oil fromconduit 134 is passed through conduits 82 and 82a to the outboard endsof cylinders 26 and 28 and cylinders 42 and 44.

Consequently, carrier 23 will be moved to the left and if spindle 13 isnot already engaged with arm 12b will quickly be so engaged and table 14will also slide to the left on guides 18 and 19. Arm 12a, after passingthrough the distance C., will engage spindle 11 which is held axiallystationary by carrier 22 and cylinders 26 and 28. This is so becausecylinders 26 and 28 are larger in diameter than cylinders 42 and 44, andthe same weld pressure from conduit 134 is applied to all the cylinders.

Rotation of spindles 11 and 13, which then are engaged with arms 12a and12b, causes the contacting material to become plastic and, when rotationis stopped, the plastic material will cool to form the weld.

In an actual operation, the variable displacement pump 130 is adjustedto provide a travel rate for carrier 23 which permits the pistons 26aand 28a to bottom out against the inboard ends of cylinders 26 and 28and also permits table 14 to abut against stops 60 and 62 before thereis any engagement between the ends of spindle 13 and arm 12b. Thisassures that for every welding cycle, initially table 14 engages stops60 and 62 and the end of spindle 1 1 is axially located at thepredetermined start position A. In addition, for various sized centeraxle housing sections 12, the adjustable stops 60 and 62 will beadjusted so that the distance C between the opposing ends of spindle 11and arm 12a is the same, i.e., approximately to inches.

lt readily may be appreciated, however, that this same result may beachieved by designing stops 60 and 62 as fixed stops and providing thatthe effective length of piston rods 30 and 32 may be varied byadjustment to achieve the desired distance C.

During the weld cycle, the carrier 23 will travel through approximately1% to 2 inches after contact between end spindle 13 and arm 12b andthereafter table 14 will travel through about if; to 1 inch. Thedisplaced plastic material between the engaging ends of spindle 11 andarm 12a and spindle l3 and arm 12b form the welds.

After a period of time, rotation of spindles l1 and 13 is stopped. Thewelds are permitted to cool, and spindles l 1 and 13 are released fromcarriers 22 and 23. Solenoids 81A and 81B are de-energized and solenoids83A, 83B and 84A, 54B are re-energized. Solenoids 82A and 82B are thenenergized to apply oil to the inborad ends of cylinders 26, 28, 42 and44 to return the carriers 22 and 23 to their retracted loading positionsready for the next welding cycle.

As the carriers 22 and 23 return to the retracted position, limitswitches LSlA and LSlB are actuated to deenergize solenoids 82A and 82B,thereby stopping the flow of oil to the inboard sides of cylinders 26,28, 42 and 44. This allows the cylinder pistons to return to the fullyretracted positions without any shock loading of the apparatus. Thestops 60, 62 and also stops 136, 138 limit the axial sliding movement oftable 14 during the stripping operation and insure that spindles 11 and13 are easily removable from carriers 22 and 23 following a weldingcycle.

It is to be understood that various modifications may be made in thedescribed system without departing from the scope of the invention. Thehydraulic control circuit of FIG. 2 is merely exemplary of a suitablecontrol system and may be readily modified to suit specific needs. Forexample, during the weld cycle after the arms 12a and 12b and endspindles 11 and 13 have been engaged, it may be desirable to provide anextremely high axial thrust via cylinders 26, 28, 42 and 44. Toaccomplish this, structural means may be readily incorporated in thecontrol system to increase the pressure in conduit 134.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. Apparatus for friction welding first and second rotating endworkpieces to opposite ends of a nonrotating central workpiececomprising a base, first and second carrier means for supporting saidfirst and second end workpieces respectively on said base, table supportmeans for said central workpiece slidably mounted on said base betweensaid first and second carrier means, means for holding said firstcarrier means substantially axially stationary on said base during aweld cycle, and means for moving said second carrier means toward saidtable means during a weld cycle, whereby during the cycle said firstrotating end workpiece mounted on said first carrier means is maintainedsubstantially axially stationary while said second rotating endworkpiece mounted on said second carrier means is moved axially intoengagement with one end of said central workpiece mounted on said tablesupport means which is then moved axially to place the other end of saidcentral workpiece into engagement with said first workpiece.

2. Apparatus as defined in claim 1, comprising first and second actuatormeans connected to said first and second carrier means, respectively,for axially displacing both said end workpieces toward said centralworkpiece, control circuit means for energizing said first actuatormeans to initially move said first end workpiece toward said centralworkpiece to a predetermined position spaced from said central workpieceand to then hold said first carrier means and end workpiecesubstantially axially stationary at said predetermined position, saidcontrol circuit means also energizing said second actuator means to movesaid second carrier means toward said table support means and cause saidsecond end workpiece to engage one end of said central workpiece andthus move said table support means toward said first carrier means sothat the other end of said central workpiece engages said first endworkpiece.

3. Apparatus as defined in claim 2, comprising first table drive meansfor initially displacing said table means toward said second carriermeans as said first end workpiece is moved to said predeterminedposition, and adjustable stop means on said base for engagement by saidtable means to establish the predetermined spacing between opposing endsof said first end workpiece and said central workpiece at the start of aweld operation.

4. Apparatus as defined in claim 3, said control circuit meanscomprising variable displacement travel pump means for activating saidsecond actuator means to cause axial movement of said second endworkpiece at a rate adjusted to permit said table means to engage saidstop means and said first end workpiece to reach said predeterminedposition before said second end workpiece engages said centralworkpiece.

5. Apparatus as defined in claim 4, comprising second table drive meansfor urging said table means toward said first carrier means during aweld cycle, with the force applied by said second table drive meansbeing approximately equal to the firction force between said slidabletable means and said base.

6. Apparatus as defined in claim 4, said control circuit meanscomprising first travel pump means for actuating said first actuatormeans and said first table drive means to move said first end workpieceand said control workpiece to their initial predetermined positions, andweld pump means for providing acutating fluid to said first and secondactuator means during the welding operation, said first actuating meansbeing larger than said second actuating means and thereby holding saidfirst carrier means and said first end workpiece axially stationary assaid second actuating means moves said second end workpiece intoengagement with one end of said central workpiece and then moves saidcentral workpiece axially so that its other end engages said first endworkpiece.

1. Apparatus for friction welding first and second rotating endworkpieces to opposite ends of a non-rotating central workpiececomprising a base, first and second carrier means for supporting saidfirst and second end workpieces respectively on said base, table supportmeans for said central workpiece slidably mounted on said base betweensaid first and second carrier means, means for holding said firstcarrier means substantially axially stationary on said base during aweld cycle, and means for moving said second carrier means toward saidtable means during a weld cycle, whereby during the cycle said firstrotating end workpiece mounted on said first carrier means is maintainedsubstantially axially stationary while said second rotating endworkpiece mounted on said second carrier means is moved axially intoengagement with one end of said central workpiece mounted on said tablesupport means which is then moved axially to place the other end of saidcentral workpiece into engagement with said first workpiece. 2.Apparatus as defined in claim 1, comprising first and second actuatormeans connected to said first and second carrier means, respectively,for axially displacing both said end workpieces toward said centralworkpiece, control circuit means for energizing said first actuatormeans to initially move said first end workpiece toward said centralworkpiece to a predetermined position spaced from said central workpieceand to then hold said first carrier means and end workpiecesubstantially axially stationary at said predetermined position, saidcontrol circuit means also energizing said second actuator means to movesaid second carrier means toward said table support means and cause saidsecond end workpiece to engage one end of said central workpiece andthus move said table support means toward said first carrier means sothat the other end of said central workpiece engages said first endworkpiece.
 3. Apparatus as defined in claim 2, comprising first tabledrive means for initially displacing said table means toward said secondcarrier means as said first end workpiece is moved to said predeterminedposition, and adjustable stop means on said base for engagement by saidtable means to establish the predetermined spacing between opposing endsof said first end workpiece and said central workpiece at the start of aweld operation.
 4. Apparatus as defined in claim 3, said control circuitmeans comprising variable displacement travel pump means for activatingsaid second actuator means to cause axial movement of said second endworkpiece at a rate adjusted to permit said table means to engage saidstop means and said first end workpiece to reach said predeterminedposition before said second end workpiece engages said centralworkpiece.
 5. Apparatus as defined in claim 4, comprising second tabledrive means for urging said table means toward said first carrier meansduring a weld cycle, with the force applied by said second table drivemeans being approximately equal to the firction force between saidslidable table means and said base.
 6. Apparatus as defined in claim 4,said control circuit means comprising first travel pump means foractuating said first actuator means and said first table drive means tomove said first end workpiece and said control workpiece to theirinitial predetermined positions, and weld pump means for providingacutating fluid to said first and second actuator means during thewelding operation, said first actuating means being larger than saidsecond actuating means and thereby holding said first carrier means andsaid first end workpiece axially stationary as said second actuatingmeans moves said second end workpiece into engagement with one end ofsaid central workpiece and then moves said central workpiece axially sothat its other end engages said first end workpiece.